The invention relates to the transfer of fluid products, liquid or gaseous, between a base and a mobile reservoir, for example a tank loaded on a lorry or on a railway wagon.
These fluid products can be of highly varied types, for example, but not limited to, petroleum products, such as in particular petrol or liquefied petroleum gas (LPG), or chemical products, in particular acids or solvents.
In practice, these fluid products are mainly liquid, but are generally in equilibrium with a gaseous phase, so that, rather than speaking of liquid products, it is more accurate to speak of fluid products. It may be necessary to transfer these two liquid and gaseous phases separately.
There are in practice various types of tank adapted to be loaded onto various types of support (lorry or wagon). In addition, the tanks are provided with connection flanges, designed to be connected to liquid product transfer pipes, which can be situated in highly diverse ways on the body of these tanks. Finally, in practice it proves to be impossible to guarantee that a mobile support, such as a lorry or wagon, carrying a tank, can always be brought exactly into the same configuration relative to a base, when a transfer operation is necessary.
This is why the connection between the base on the one hand and the connection flange on the mobile reservoir on the other hand can be effected only by means of a device having a certain deformation capability. The fluid product transfer devices, often referred to as transfer arms or loading/unloading arms, are thus of two possible types: either they have a flexible part, which poses possible problems of resistance to aging, or they are constituted by a succession of at least two tubular sections articulated on each other.
Fluid product transfer arms must therefore in practice be brought into a suitable configuration when a transfer operation is being prepared, so as to bring a free end of this arm (the other end generally being connected permanently to the base) opposite the connection flange of the tank concerned. This operation is generally carried out by an operator, and it is desirable for the latter not to be obliged to deploy excessively high forces. It should be stated here that motorized control of a liquid product transfer arm, which avoids any effort for the operators, is however difficult to implement, having regard to the difficulty in bringing the free end of the arm, in an automated fashion, precisely opposite the connection flange; this assumes a high degree of control with regard to the automatic controller controlling the configuration of the arm, and therefore possibly long and expensive training for the operator. In any event, such motorized control entails high costs.
To avoid an operator having to deploy major forces during the manual maneuvering of a liquid product transfer arm, various types of balancing device have already been proposed, designed to compensate at least partly for the variations in torque about the articulation axes (essentially about the horizontal axes due to gravity) generated by the movements of the masses during variations in configuration of the tubular sections of the arm about the axes.
A first category of balancing device uses one or more counterweights which are fixed opposite the part of the arm to be balanced. This solution, entirely effective, nevertheless proves bulky in practice.
Another category of balancing device uses springs, for example steel torsion springs, usually in a cylindrical helix, attached to the rotating joint or inside it. They may also be steel torsion springs in an Archimedes spiral or in a hyperbolic spiral.
Another category of balancing device uses a steel compression spring, often situated along the part of the arm to be balanced or in an appliance referred to as a balancing box or spring box, fixed to the arm part to be balanced.
Yet another category of balancing devices uses steel draw springs also often situated along the arm.
Another configuration of balancing devices uses jacks, for example nitrogen, pneumatic, hydraulic or electric cylinders.
Naturally, these various types of balancing are not mutually exclusive and it has already been proposed to combine several types of balancing on the same transfer arm.
These various solutions have their inherent advantages and disadvantages. It can however, in summary, be stated that at the present time there exists no balancing device which is at the same time effective, compact, reliable and inexpensive, all over a wide range of movement. Thus, for example, the presence of counterweights (see above) provides effective balancing, in a wide variety of possible positions, but at the cost of considerable bulk. With regard to the other solutions, the quality of the balancing is generally entirely approximate, in particular when the transfer arm in question is designed to allow significant movement, in practice on each side of a horizontal idle configuration (there is not always symmetry on either side of this horizontal configuration) and often turns out to lead to risks of faulty operation, having regard to moving parts. Finally, the complete range of movement in which the balancing is satisfactory is generally 40-50xc2x0 at most.
A subject of the invention is to overcome the aforementioned drawbacks.
To this end it proposes an articulated arm for transferring fluid products, liquid or gaseous, having: two tubular sections connected to each other by a rotating joint with a horizontal axis, and one of which, rotationally mobile about this horizontal axis, has an angular reference configuration in which it is in equilibrium despite the effect of gravity; and a balancing device to compensate for the variations in the gravitational effect on this mobile tubular section as a function of the orientation of this vis-a-vis the vertical, characterized in that this balancing device is mounted between a reference portion fixed relative to the axis of rotation of the rotating joint and a linkage portion of the mobile tubular section which is at a distance other than zero from the axis of rotation and includes a spring which tends to return the mobile section to its angular reference configuration, this spring being designed and mounted so as to apply to the mobile tubular section a force which is approximately proportional to the distance between this linkage portion and the position occupied by this linkage portion when the mobile section is in its angular reference configuration, this spring being in an idle configuration when the mobile section is in a balancing configuration relative to the axis of the rotating joint.
It should be remembered here, that a person skilled in the art usually designed these balancing devices from an intermediate configuration, within the complete range of movement, so as to act upon the spring in both directions, taking advantage of a certain behavioral symmetry of the spring, and thus maximizing the angular amplitude of effectiveness of this spring (a spring generally retains linear characteristics within a limited range about its idle configuration). On the other hand, the invention teaches to choose this reference configuration independently (even from outside) of the range of movement. The result of this is a balancing device which is compact, simple and inexpensive and effective within a quite substantial range. As will be seen, this type of balancing allows good performances, even with significant movements by choosing springs of suitable design.
Preferably, the other section has an orientation which is fixed relative to the axis of the rotating joint (frequently in practice it is the section connected to the fixed base) and the fixed reference portion to which the balancing device is connected by one of its ends is integral with this fixed section. This allows the bulk of the balancing device to be minimized.
Advantageously, the balancing device is connected to this fixed reference portion and the linkage portion of the mobile section by articulations with horizontal axes, which, when the balancing device is not flexible, minimizes the parasitic torque about the rotational axis of the rotating joint.
It is quite particularly useful to provide for the fixed reference portion to be approximately arranged opposite, parallel to the axis of rotation, to the position into which the linkage portion of the mobile tubular section moves, when this is in its reference configuration. This contributes to approaching a very good linearity of the spring as a function of the angular amplitude of the rotation of the section to be balanced. In fact, during the rotation of the tubular section to be balanced, the distance to the axis (lever arm) of the restoring force applied by the spring varies in the same manner as the distance to the axis of the weight.
According to a particularly advantageous embodiment, the balancing device is in the shape of a loop, situated in a plane approximately perpendicular to the axis of rotation and elastically deformable in this plane and has two ends which are, in the idle configuration of this spring, close to one another. This contributes to combining the aforementioned advantage of the good linearity with compactness. In a particularly simple embodiment, the spring comprises: a U-shaped piece forming the spring, elastically flexible in the plane of the loop and having two legs connected by a curved portion; and two fastening lugs extending these legs to the ends of this balancing device.
It should be noted here that the spring advantageously comprises a single loop, for reasons of simplicity, but that, if a greater bulk is allowed parallel to the axis of rotation, springs comprising several loops or turns can be chosen (this can produce a lower stiffness when this is desired).
Good linearity, low parasitic torque and compactness are combined when the balancing device is, at its ends, connected to the fixed reference portion and to the linkage portion of the mobile tubular section, by articulations with axes which are parallel to the axis of rotation of the rotating joint.
The linearity is very good when the ends of the balancing device are opposite, parallel to the axis of rotation of the rotating joint.
Very generally, it is particularly simple to choose a spring which is generally Ushaped, within a balancing device of whatever design. Thus, for example, it can also be a device in which one of the ends of the spring is connected to the linkage portion of the mobile section by a belt passing through a pulley situated, parallel to the axis of rotation, opposite the position in which the linkage portion of the mobile tubular section is found when this is in the reference configuration.
It will be appreciated that in a balancing device according to the invention the spring legs (whether U-shaped or more generally in the shape of one or more loops) are acted upon in a single direction throughout the movement of the mobile section, preferably in the direction corresponding to a coming together (sometimes described as xe2x80x9ccompressionxe2x80x9d of the spring with legs).
According to other preferred arrangements of the invention, optionally combined:
the U-shaped or not U-shaped spring is made from composite material;
the U-shaped or not U-shaped spring is covered with a silicone sheath.